Lead is an essential commodity in the industrialized world, ranking fifth in tonnage of metals consumed, after iron, copper, aluminum, and zinc. The principal uses of lead and its compounds are storage batteries, tetraethyllead for increasing octane rating of gasolines, pigments, ammunition, solders, plumbing, cable coverings, bearing, and caulking. Because of its softness and high density, lead is an ingredient in many alloys.
However, lead and its compounds are cumulative poisons, and should not come into contact with food and other substances that may be ingested. Lead enters the body through inhalation and ingestion, is absorbed into the circulatory system from the lungs and digestive tract, and excreted via the urine and feces. Normally, intake of lead approximately equals output. However, excessive exposure and intake of lead can upset the balance and cause tissue concentrations to increase to the point where illness can result. Symptoms of lead poisoning include anemia, fatigue, headache, weight loss, and constipation. More sever manifestations include damage to the nervous system and to the kidneys.
The particle size and chemical composition of lead and lead compounds affect the readiness with which lead is absorbed from the lungs and digestive tract. Larger particles and compounds with lower solubility are less hazardous than finely divided particles and compounds of higher solubility.
Because lead may be ingested and inhaled, and because particle size and chemical composition affect its absorption, it is important that the concentration of lead in the environment be limited as much as possible.
Because lead has been found to be particularly dangerous in the environment, the use of lead as an additive in automobile fuels has been sharply curtailed. However, there is still a great deal of lead present as waste in the environment. For example, there is a great deal of sand containing lead oxide paint chips recovered from sandblasting operations, and there are many soils contaminated with lead from battery disposal or manufacturing operations.
A number of methods have been developed to deal with disposal of hazardous metal wastes. However, most of these methods are costly and do not produce useable end products.
Osgood, in U.S. Pat. No. 1,169,506, discloses a process for treating slag which may contain lead by heating small particles of the slag in the presence of a more easily fusible silicate and further treating the particles either with other fusible salts or with a coloring material. The slag consists largely of silica with a greater or lesser percentage of calcium oxide or other relatively refractory oxides.
Dunn, in U.S. Pat. No. 1,962,270, discloses a method for treating slags, including lead slags, by mixing one equivalent of silica with one equivalent of base, and heating the mixture in a reducing atmosphere. Metallic impurities can be removed by skimming the surface of the molten slag. Sulfur is removed as sulfides, which are produced in the reducing atmosphere of the heating process. Sand or other minerals can be added to the slag, which effects some chemical combination with the molten silicates in addition to the mechanical admixture. The treated slag can be used as a binding agent or cement for small sized materials to form a type of concrete.
Roberts et al., in U.S. Pat. No. 4,678,493, disclose a method for vitrifying asbestos waste by combining the asbestos with waste glass and a melt accelerator to dissolve the asbestos and to produce a homogeneous glass.
Nye, in U.S. Pat. No. 2,217,808, discloses a method for converting furnace slag into a glasslike composition by taking molten slag as it emerges from a blast furnace and adding silica thereto to form an improved glasslike material.
Colwell, Jr. et al., in U.S. Pat. No. 4,632,690, disclose a method for removing hazardous waste comprising impinging a flame on a surface of molten mass material, injecting into the molten mass solid or sludge type hazardous or toxic waste material, heating the molten mass by the flame, and transferring the molten mass from the melting chamber to the refining chamber upon destruction of certain hazardous or toxic waste material embodied therein. The product is a glasslike material. This system provides for destruction of toxic wastes by pyrolysis and/or combustion, which would not destroy the toxicity of lead-containing waste.
Wheeler, in U.S. Pat. No. 4,820,325, discloses a method for treating a filter cake impregnated with a toxic material comprising heating the filter cake, which is formed of a glass precursor material, with at least one other glass precursor material, at sufficiently high temperatures to form a molten composition which solidifies upon cooling to form a glass. The glass can be disposed of without danger of the toxic material leaching out.
Meininger et al., in U.S. Pat. No. 4,581,163, disclose a method for conditioning weakly to medium-active wastes through fused vitrification by means of electrodes which generate the melting heat. The waste, with optional additive materials such as silicates in the form of clay dust, quartz sand, and diatomaceous earth, is fused to form a glassy product.
Cadoff et al., in U.S. Pat. No. 4,759,879, disclose an alkoxide glass formed composition including silica-containing constituents, which can be used for the immobilization of nuclear waste.
Japanese Patent No. 62-232600 discloses a method for disposing of material containing zirconium or a zirconium alloy by adding a eutectic and compressing the material to form a coiled material. The coiled material is put into a crucible and heated to 1000.degree.-1200.degree. C. to melt the material and dispose of the zirconium.